1. Field of the Invention
The present invention relates to a nitride-based semiconductor light emitting diode (hereinafter, referred to a nitride-based semiconductor LED) which can implement high luminance by improving the electrode structure of the nitride-based semiconductor LED.
2. Description of the Related Art
Generally, nitride-based semiconductors are group III-V semiconductor crystals having a compositional formula of AlXInYGa1−X−YN (0≦X≦1, 0≦Y≦1, 0≦X+Y≦1). The nitride based semiconductors are widely used as LEDs that emit short wavelength light (ranging from ultraviolet light to green light), especially blue light.
The nitride based semiconductor LEDs are manufactured by using an insulating substrate, such as a sapphire substrate or SiC substrate, which meets a lattice matching condition for crystal growth. Two electrodes connected to p-type and n-type nitride semiconductor layers, respectively, have a planar structure. In such a planar structure, the two electrodes are arranged almost horizontally on an emission structure.
The nitride based semiconductor LEDs having the planar structure must have high luminance when they are to be used as a lighting source. In order to obtain the high luminance, large-sized nitride based semiconductor LEDs are manufactured which uniformly spread a current so as to increase light-emission efficiency.
However, compared with nitride based semiconductor LEDs having a vertical structure where two electrodes are respectively arranged on the top and bottom surfaces of the emission structure, the nitride based semiconductor LEDs having the planar structure have non-uniform current flow in an entire emission region. Thus, the effective area used for light emission is not so wide that the emission efficiency is low.
Hereinafter, the problems of the large-sized nitride based semiconductor LED having the planar structure according to the related art will be described with reference to FIGS. 1 and 2.
FIG. 1 is a plan view illustrating the structure of a conventional nitride-based semiconductor LED, and FIG. 2 is a sectional view taken along II-II′ line of FIG. 1.
As shown in FIGS. 1 and 2, the nitride-based semiconductor LED having a planar structure includes a buffer layer 110, an n-type nitride semiconductor layer 120, a GaN/InGaN active layer 130 having a multi-quantum well structure, and a p-type nitride semiconductor layer 140, which are sequentially formed on a sapphire substrate 100. Portions of the p-type nitride semiconductor layer 140 and the active layer 130 are removed by a mesa-etching process such that a portion of the top surface of the n-type nitride semiconductor layer 120 is exposed.
On the exposed n-type nitride semiconductor layer 120, an n-type electrode pad 160a and an n-electrode 160 extending from the n-type electrode pad 160a in one direction are formed.
On the p-type nitride semiconductor layer 140, a transparent electrode 150 composed of ITO (indium tin oxide) or the like is formed. On the transparent electrode 150, a p-type electrode pad 170a, a p-type connection electrode 170′ extending from the p-type electrode pad 170a in either direction, and a p-electrode 170 extending from one end of the p-type connection electrode 170′ are formed.
More specifically, the p-electrode 170 of the conventional nitride-based semiconductor LED having a planar structure is formed to have a finger structure where the n-electrode 160 is surrounded by the p-type connection electrodes 170′ extending from the p-type electrode pad 170a in both directions. Therefore, in the nitride-based semiconductor LED, the p-electrode 170 and the n-electrode 160 are spaced from each other at the most uniform distance on the entire surface of the diode, thereby uniformly spreading a current flow in the overall light-emission region of the diode.
In this case, the p-electrode 170 and the p-type connection electrode 170′ of the conventional nitride-based semiconductor LED are formed along the outermost side of the transparent electrode 150. Therefore, as shown in “A” portion of FIG. 1, the p-electrode 170 and the p-type connection electrode 170′ form a perpendicularly-bent portion in the corner of the transparent electrode 150 where the p-electrode 170 and the p-type connection electrode 170′ are joined to each other.
As described above, however, when the p-electrode 170 and the p-type connection electrode 170′ form a perpendicularly-bent portion in the corner of the transparent electrode 150, a current is crowded in this bent portion, thereby reducing a characteristic and reliability of the LED.
Further, in the conventional nitride-based semiconductor LED, the n-electrode 160 extending from the n-type electrode pad 160a toward the p-type electrode pad 170a reflects some of light emitted from the active layer 130 such that a light-emitting surface corresponding to a portion where the n-etectrode 160 is positioned is diminished, as shown in “B” portion of FIG. 2. As a result, the overall luminance of the LED is reduced.